Carbon nanotubes (NTs) have received significant attention for technological applications because of their desirable properties, which include high electrical conductivity, high carrier mobility, and high mechanical strength; and due to their ability to be processed into various forms such as fibers and thin films. NTs in the form of networks and films have been proposed as electrodes for several types of devices, including: polymeric supercapacitors; transparent electrodes for organic light emitting diodes and organic photovoltaic devices; and organic electrodes for organic light emitting diodes, organic photovoltaic devices, and organic electrochromic devices. NT dispersions within an electroactive organic matrix, such as, poly(3-alkylthiophene)s and poly(phenylene vinylene)s, have demonstrated a potential to act as an electroactive component within a bulk heterojunction photovoltaic device. Recent work has demonstrated that dispersing NTs within an organic polymeric matrix, such as polystyrene and a polyacrylate, dramatically increases its strength, toughness, and durability in addition to its introduction and augmentation of other properties. Therefore, dispersion of NTs into electroactive organic materials is promising as active sites of: charge storing supercapacitors/batteries; solar cells; electrochromic fiber and film-based devices; and light emitting devices, which, aside from producing enhanced electronic properties, can result in durable and robust materials.
Critical to the commercial success of NT films is an ability to process the films on a large scale via methods such as printing, roll-to-roll coating, and spraying. Such processing methods require solutions or suspensions of NTs that are well-dispersed and where the homogeneous solution or suspension can be maintained for an extended period of time. Examples of such carbon NT dispersants include ionic and non-ionic surfactants, DNA, conjugated polymers, and non-conjugated polymers that contain polycyclic aromatic groups, such as pyrene and porphyrins. NT films for high-end electronic applications require a low sheet resistance (<300 Ohms/sq) and, for those applications involving transparent electrodes, the low sheet resistance must be accompanied by a high transmittance (above 75%) of electromagnetic radiation in the wavelength region of interest. However, NT thin films that have been deposited as dispersions, using techniques that are amenable to large scale production, have resulted in sub-optimal transparency and/or conductivity, usually with a resistivity above 1,000 Ohms/sq when having acceptable transmittance levels. Many dispersants, especially polymeric dispersants, have been designed to blend NTs into polymer composites as reinforcement materials but are not appropriate for the formation of transparent conductive thin-film electrodes. Typically, NT dispersants are irreversibly bound to the nanotubes, where the NT dispersant exceeds the content of the NTs in the thin film and have not demonstrated the capability for use in high-end electronic applications.
Therefore, a need remains for a NT dispersant that allows the formation of a stable dispersion of carbon NTs and that can be easily removed to form a thin film without damaging or detracting from the structure and properties possible for NTs. Additionally, these dispersants would be useful for formation of nanotube composite materials for electroactive and related devices including: electroluminescent devices; photovoltaics; electrochromic films and fibers; field-effect transistors; batteries; capacitors; and supercapacitors.